Emerald Group Publishing Limited
Copyright © 2000, MCB UP Limited
CMMs keep airline operating safely
Keywords LK, Measuring machines
Near perfection in the design, manufacture and assembly of parts is essential to keeping a jet flying safely miles above the earth for up to 20 hours a day. That is why nearly every component which makes its way into an aircraft operated by United Airlines in the USA, from turbine blades to food trays, is meticulously inspected on co-ordinate measuring machines CMMs built by LK, a UK firm based in Donnington, Derbyshire.
Art Mehlhaiff, inspection co-ordinator and team leader at United Airlines' San Francisco plant, is of the opinion that CMMs greatly reduce the risk of integrating an imperfect part into an engine. He said, "Our engineering department determines which parts are to be measured on a CMM, driven largely by the tolerances which are needed to achieve optimal engine performance - a key factor in the profitability of operating an aircraft.
"For instance, if the clearance is too large between the compressor casing and the rotating blades, the engine will run hot, which can lead to poor performance, increased friction, higher fuel bills and finally even engine failure."
After buying its first LK measuring machine in the early 1980s, United Airlines decided to standardise its measuring procedures by integrating four additional CMMs from the same manufacturer into its maintenance operations centre. Three are in an inspection department primarily involved with final inspection of engines and their component parts. The other two machines are used in a metrology lab for inspecting incoming tooling, calibrating fixtures and general research and development work.
It is the measurement and quality control of remanufactured engine parts, however, which provides United Airlines with the biggest savings. If a component has not been machined to the tolerances originally specified, the exact degree of error is printed out by the LK machine and presented to the engine OEM. It can then determine the cause of the problem and improve its process to meet the airline's specifications.
United estimates that it saves nearly US$500,000 and quite a few engines each year by using LK machines to detect out-of-tolerance parts prior to the assembly and testing stage. In addition, the CMMs have obviated the need for expensive fixturing and other bespoke tooling required for routine measurements on a number of production engines. This has saved the company millions of dollars in fixturing costs and freed a significant amount of space on the shopfloor.
Another use for the measuring machines recently presented itself to United Airlines. One of its suppliers announced that it would no longer provide hard gauge fixtures for fan blades used in future engines. Such fixtures are traditionally required to return the blades to their original tolerances during routine remanufacture or repair. Harsh weather conditions at high altitude and bird strikes during takeoff and landing make such blade reprofiling a not infrequent event. United Airlines does not have to subcontract gauge manufacture to outside specialists which charge premium rates; the blade profiles are held electronically and the gauges are produced in-house using an LK CMM to verify their accuracy.
Vic Cleland, metrologist and CMM calibrator at the San Francisco factory, says that the metrology lab measuring machines are also saving the company money, particularly in R&D. Parts that used to take two to three days to inspect with special fixturing can now be measured in just a few hours using one of the CMMs. It is reported that labour costs have plummeted in line with the cycle times.
To streamline further its inspection procedures, United Airlines is in the process of connecting its CMMs to a central server which will enable operators to access the complete library of programs for all component parts of an aircraft. Using the DMIS protocol, LK's "CAM 10" CAD-to-CMM interface software will provide the operator with component set-up information: and graphical reporting for the automatic production of full colour, illustrated inspection reports. Regardless of how obscure a part might be, a vast database can be interrogated to determine if a specific program exists for inspecting it.
Details available from: LK Limited. Tel: +44 (0) 1332 811349; Fax: +44 (0) 1332 850149.